1. Field of the Invention
The present invention relates generally to a method and apparatus for the completion of multilateral wells, that is, when one or more lateral wells are drilled from a primary well bore, and more particularly to a new and improved method and apparatus for a junction between the primary well bore and a lateral well bore.
2. Background of the Invention
Multiple lateral bores are typically drilled and extended from a primary or main well bore. The main well bore can be vertical, deviated, or horizontal. Multilateral technology can be applied to both new and existing wells, and provides operators several benefits and economic advantages over drilling entirely new wells from the surface. For example, multilateral technology can allow isolated pockets of hydrocarbons, which might otherwise be left in the ground, to be tapped. In addition, multilateral technology allows the improvement of reservoir production, increases the volume of recoverable reserves, and enhances the economics of marginal pay zones. By using multilateral technology, multiple reservoirs can be produced simultaneously, thus facilitating heavy oil production. Thin production intervals that might be uneconomical to produce alone become economical when produced together with multilateral technology. Consequently, it has become a common practice to drill deviated, and sometimes horizontal, lateral boreholes from a primary wellbore in order to increase production from a well.
In addition to production cost savings, development costs also decrease through the use of existing infrastructure, such as surface equipment and the well bore. Multilateral technology expands platform capabilities where space is limited, and allows more well bores to be added to produce a reservoir without requiring additional drilling and production space on the platform. In addition, by sidetracking depleted formations or completions, the life of existing wells can be extended. Finally, multilateral completions accommodate more wells with fewer footprints, making them ideal for environmentally sensitive or challenging areas.
The primary wellbore may be sidetracked to produce the lateral borehole into another production zone. Further, a lateral wellbore may be sidetracked into a common production zone. In sidetracking, a whipstock and mill assembly is used to create a window in the wall of the casing of a wellbore. The lateral wellbore is then drilled through this window out into the formation where new or additional production can be obtained.
One of the objectives of a multilateral well is containment of the surrounding formation. Production from a lateral borehole can be difficult if the lateral borehole is drilled through a loose or unconsolidated formation. If the lateral borehole is drilled through an unstable or unconsolidated formation, the formation will tend to cave into the borehole. The formation can also slough off, causing deleterious debris to mix with the production fluids. Thus, it is preferred to contain the formation to prevent cave-ins and slough-offs.
Formations that contain a significant amount of shale can be a particular problem. If the bore surfaces at and near the junction are not covered with a liner, chips and aggregate in this area tend to be drawn into the produced fluids and foul the production. Unfortunately, lining the bore surfaces near the junction can be complex and time consuming. Various devices have been proposed to provide a junction at the interface of the primary and lateral wellbores.
There have been attempts to use a perforated insert through the window to allow production from both the primary bore and lateral bore while reducing contamination from chips and aggregate. The perforations are aligned with the primary bore and fluid from the primary bore passes through the perforations. Unfortunately, the perforations tend to become clogged by the chips and aggregate and allow the chips and aggregate to contaminate the product, thereby reducing the effectiveness of this type of insert. Also, the use of a perforated insert hinders the ability to reenter the main bore below the junction.
The junction of the lateral borehole with the primary wellbore is usually ragged and rough as a result of the milling of the window through the casing to drill the lateral borehole. It is particularly difficult to seal around the window which is of a peculiar shape and has a jagged edge around its periphery.
A large area is exposed to the formations when the window is cut in the casing. A tie-back assembly may be disposed adjacent the junction of the lateral borehole and primary wellbore. See for example U.S. Pat. No. 5,680,901. The tieback assembly and liner limit the exposure of the formation through the window cut in the casing.
U.S. Pat. No. 5,875,847 discloses a multilateral sealing device comprising a casing tool having a lateral root premachined and plugged with cement. A profile receives a whipstock for the drilling of the lateral bore hole through the lateral root and cement plug. A lateral liner is then inserted and sealed within the lateral root.
TAML (Technology Advancement Multi-Lateral) defines six levels for a multi-lateral junction for a lateral borehole. For example, level three merely includes a junction with the main casing and a liner extending into the lateral borehole without cementing or sealing the junction. If the liner is merely cemented at the junction, it is a level four since cement is not acceptable as a seal. Level four simply includes cement around the junction. Level five requires pressure integrity at the junction.
Prior art multilateral wells are sealed with cement using a method well-known to those with skill in the art and described hereinafter.
Level five includes seals used to achieve pressure integrity around the junction. For example, in level five, separate tubulars extend through the main borehole and through the lateral borehole. A packer is placed around the upper ends of these tubulars to pack off with the casing of the cased main borehole. The lower end of the tubular extending through the main tubular includes a packer for sealing with the main tubular below the junction, and the lower end of the other tubular extending through the lateral borehole seals with an outer tubular in the lateral borehole below the junction. The lateral borehole preferably has been previously cased so that a seal can be set with that tubular extending into the lateral borehole. Since there are separate tubulars and both bores are now packed off, there can be independent production from each bore without commingling. The pair of tubulars above the junction may extend all the way to the surface, or one well may be produced through a production pipe extending to the surface and the other well may be produced through the annulus formed by the casing and the production pipe extending to the surface.
Where the formation pressure is substantially the same in the pay zones being produced by the main and lateral boreholes, the hydrocarbons from the main and lateral boreholes may be commingled. However, it is sometimes desirable to separate production so that each well can be independently controlled, such as where the pay zone pressures are different. In that case, separate tubulars are used to produce the individual wells, as previously described in a level five junction, or one well may be plugged off if necessary. Whether production is commingled or independent has no bearing on how a multilateral well is classified.
If the formation is a solid formation, the lateral borehole, for example, need not even include a casing or liner and may be produced open hole. If the lateral borehole is unconsolidated or unstable and would tend to cave in, the lateral borehole would be cased off or include a liner to contain the formation. For example, it is common in the prior art to run and set a liner in the lateral borehole with the liner extending from the flowbore of the casing and down into the lateral borehole. Cement is then pumped down through the cased main borehole, across the junction into the lateral borehole below the junction, and into the lateral borehole both inside and outside the liner. Then, the bore of the cased main borehole is cleaned out by drilling out the cement, including milling off that portion of the liner extending into the bore of the cased main borehole, leaving an exposed end of the liner at the junction which extends into the lateral borehole. The liner is then cleaned out giving access to both the main and lateral boreholes. This procedure is tedious and includes the problem of the drill tending to enter the liner as it removes the cement and liner end from the main borehole. This method is also problematic because the cement acts as both the junction and the seal. The cement is subject to failure due to limitations in the cement material itself or the ability to place the cement successfully at the junction. More particularly, under downhole conditions, cement can fail by deteriorating to such an extent that the seal begins to leak thus contaminating the production fluids.
An alternative to the above-described method is described in pending U.S. patent application Ser. No. 09/480,073, filed Jan. 10, 2000 and entitled xe2x80x9cLateral Well Tie-Back Methods and Apparatus.xe2x80x9d A lateral well tie-back apparatus and method is used to help ensure adequate flow and production from a lateral bore.
There are a variety of additional configurations that are possible when performing multilateral completions. For example, U.S. Pat. No. 4,807,704 discloses a system for completing multiple lateral wellbores using a dual packer and a deflective guide member. U.S. Pat. No. 2,797,893 discloses a method for completing lateral wells using a flexible liner and deflecting tool. U.S. Pat. No. 3,330,349 discloses a mandrel for guiding and completing multiple lateral wells. U.S. Pat. Nos. 4,396,075, 4,415,205, 4,444,276, and 4,573,541 all relate generally to methods and devices for multilateral completion using a template or tube guide head. For a more comprehensive list of patents, U.S. Pat. No. 6,012,526 details these configurations and presents a patent literature history of the well-recognized problem of multilateral wellbore completion.
Notwithstanding the above-described attempts at obtaining cost effective and workable lateral well completions, there continues to be a need for new and improved methods and devices for providing such completions, particularly sealing between the juncture of primary and lateral wells, the ability to re-enter lateral wells, particularly in multilateral systems, and achieving zone isolation between respective lateral wells in a multilateral well system. The present invention relates to a new and improved method and apparatus for the construction and completion of a multilateral well junctions, and overcomes the deficiencies of the prior art.
A junction for the intersection of a main borehole and a lateral borehole includes a main tubular having a main window with a ramp aligned with the main window, and a lateral tubular adapted to be telescopingly received within the main tubular and having a lateral window. The main tubular and lateral tubular each have an orientation surface. The lateral tubular has a first position with one end partially disposed within the main tubular. The lateral tubular is telescoped into the main tubular with the end of the lateral tubular engaging the ramp which guides the end of the lateral tubular through the main window and into the lateral bore. The orientation surfaces engage to orient the lateral window with the main window and form a common opening between the tubulars. The ramp is preferably an arcuate surface at an angle to the axis of the main tubular and extends along the edges of the main window between the inner and outer diameters of the main tubular. The orientation surfaces are preferably mule shoe surfaces which engage to rotate the tubulars into alignment.
The junction may also include a shear member to releasably connect the lateral tubular within the main tubular until the junction is to be deployed. Once the lateral tubular is released, preferably by shearing the shear member, it telescopes down into the main tubular until the lateral tubular reaches the ramp adjacent the main window. The ramp deflects the lateral tubular out through the main window by engaging the end of the lateral tubular. The lateral tubular has one end extending from the main tubular to form the junction between the lateral borehole and the primary borehole. The main tubular extends into the main borehole and the lateral tubular extends into the lateral borehole.
The present invention is also directed to a method of multilateral well completions. To create a lateral well bore, a milling assembly is run into the main well bore to a desired depth and orientation. An anchor and/or packer are set. If a well reference member is not previously set, a reference member may also be set on the same run. A window is milled in the cased borehole and a lateral rat hole is drilled. The milling assembly and whipstock are then removed. The junction with main tubular and lateral tubular is run into the main bore in substantial alignment. The lateral tubular is partially disposed within the main tubular and is releasably held by a shear member. The main window becomes aligned with the lateral rat hole when an orienting member at the bottom of the main tubular engages the downhole well reference member, thereby rotating and orienting the junction assembly.
A weight is applied to the lateral tubular causing the lateral tubular to disengage the main tubular allowing the lateral tubular to be received within the main tubular. Any misalignment that occurs while the lateral tubular is deflected out of the main window via the ramp is corrected when the lateral orientation member engages the orientation surface of the main tubular. When the lateral orientation member and the main orientation surface are fully engaged, the lateral and main windows are substantially aligned and facing each other to form the junction.
There are many benefits to using the present invention. Critical work is done prior to exposing the time dependent formations. A level four multilateral well can be achieved without milling excess liner. A minimal amount of cementing is required, although cementing is optional for the present invention. The access diameters for both the main and lateral tubulars are maximized. The present invention allows re-entry capabilities in both bores.
Other objects and advantages of the invention will appear from the following description.